The present invention relates to telecommunication techniques. More particularly, the present invention provides a method of improving broadband variable gain amplifier (VGA) with stable frequency response for different gain settings.
Over the last few decades, the use of communication networks exploded. In the early days Internet, popular applications were limited to emails, bulletin board, and mostly informational and text-based web page surfing, and the amount of data transferred was usually relatively small. Today, Internet and mobile applications demand a huge amount of bandwidth for transferring photo, video, music, and other multimedia files. For example, a social network like Facebook processes more than 500 TB of data daily. With such high demands on data and data transfer, existing data communication systems need to be improved to address these needs.
Over the past, high data rate broadband communication has been widely implemented via optical network, in which data signals are carried by laser light that is specifically modulated using various kinds of electro-optic modulators. Through communication systems for transmitting the high-data rate signals, variable gain amplifier (VGA) is widely applied. But designing a VGA whose frequency response changes within a tolerable variation for a large gain range is challenging. Conventional designs usually come with power and/or area penalties for large gain setting. For example, a common approach is to identify the gain range with stable frequency response. If the range is not sufficient, the controlled gain range is extended by cascading another VGA. This increases area and power consumption and reduces the overall frequency response. Alternatively, another approach is to compensate for the frequency response variation once the gain is set to a value that exceeds a determined gain range. With this approach, a frequency dependent stage can compensate for losses, but this increases complexity and/or power consumption.
Therefore, an improved VGA design with stable frequency response for widened gain control range is desired.